Piezoelectric conversion system



INVEN H. ANDO 6 ,2 g Q 5 P o 5 e 1- E R Filed Jan. 5, 1939 July 15,1941.

PIEZOELECTRIC CONVERSION-SYSTEM Patented July 15, 1941 UNITED STATESPATENT OFFICE PIEZOELECTRIC CONVERSION SYSTEM Hiroshi Ando, Tokyo-Shi,Japan Application January 5, 1939, Serial No. 249,543

2 Claims.

This invention relates to improvements in piezo-electric conversionsystems, and has for its object to remove a heretofore unknown cause ofthe element of the piezo-electric conversion system becominginoperative.

The accompanying drawing illustrates an embodiment of the inventionwherein the circuits of the piezo-electric device are showndiagraminatically.

Heretofore, the use of Rochelle salt has been well known for apiezo-electric element. This kind of material has a piezo-electriccharacter above a thousand times larger than that of chemically stablematerial, such as quartz and tourmaline, and the mechanical resonanceproduced therein is less sharp than that produced in quartz, ortourmaline. In these respects, the material, such as Rochelle salt, canbe advantageously used for a piezo-electric transducer but has thefollowing drawbacks:

1. There is unproportional relation between pressure and voltage likehysteresis in magnetic circuits.

2. The material per se is still too sharp in resonance.

3. The material eilioresces or deliquates.

l. There is a surface leakage on the material.

5. The mechanical impedance of the material is too high.

I have found that all of these drawbacks are removed by selectingRochelle salt elements with regard to their special shape and theelasticity of electrode, and further by applying a special surface skinand special fillings to said elements. I have, however, found that someof such piezoelectric transducers become inoperative in a short periodof time, and I have found that the inoperativeness is caused by the fallof the internal resistance of the transducer elements. For example, withthe transducer element having an original internal resistance of 700,000ohms, I experienced that the internal resistance is reduced severalthousand ohms to 10,000 ohms when it has become degraded in itscharacter and has become inoperative. There is no doubt that it is notdue to the matters given in the afore-mentioned items 3 and 4 in view ofthe same phenomenon being observed when operating the transducer elementin oil protected with a special surface skin and special fillings.

According to the present application, the electrodes of a Rochelle saltpiezo-electric transducer are shunted by means of a high resistance forthe dissipation of static charges thereof, and these electrodes areseparated from the output circuits thereof by means of a series con-'denser having a capacity not preventing low frequency output of saidconverter, instead of leading the electrodes direct to the outputcircuit, and the output side passed through said condenser is lead tothe output circuit by means of a well known potentiometer, or by meansof other means. The value of the high resistance for the static chargedissipation determines the low frequency characteristic and the highfrequency characteristic, and the potentiometer regulates the outputvoltage.

Referring to the accompanying drawing, I represents a piezo-electrictransducer and 2 R0- chelle salt elements thereof. Two electrodes of thetransducer are shunted by means of the high resistance Re for thedissipation of static charge of said transducer. The high value of thisresistance is favourable for low-frequency conversion, but unfavourablefor high-frequency conversion, and the low value of this resistance isfavourable for high-frequency conversion, but unfavourable forlow-frequency conversion. A suitable value is, therefore, given to thisresistance, and a series condenser 5 is inserted between the transducerand its output side 0, which has a capacity not preventing low-frequencyoutput of said transducer. For example, with the internal capacity ofthe converter of 0.01 microfarad, the capacity of said series condenseris preferably of the order of 0.03 microfarad. The output is leadthrough said condenser to the output side 0 and if necessary through apotentiometer P. The transmission member 6 for mechanical movement maybe connected to a diaphragm, or stylus carrying device by suitablemeans, to constitute a microphone or pick-up. The transducer and theseries condenser 5 may be conveniently mounted in a casing 1.

From the foregoing, it will be understood that the present inventionprovides a great advantage to the practical use or this kind of thepiezoelectric transducer, the effect being brought about to removeheretofore unknown cause of a transducer becoming inoperative.

I claim:

1. A piezo-electric conversion system comprising, two Rochelle saltplates, an electrode between said plates, electrodes arranged alongouter faces of the plates, means electrically connecting said outerelectrodes, a relatively high resistor shunted across an outer electrodeand the central electrode for dissipating static charges thereof, an

output circuit extending from the central electrode and one of the outerelectrodes, and a condenser arranged in series circuit relation in saidoutput circuit beyond the resistor shunt.

2. A piezo-electric conversion system comprising, two Rochelle saltplates, an electrode between said plates, electrodes arranged alongouter faces of the plates, means electrically connecting said outerelectrodes, a relatively high resistor connected across the outerelectrodes and the 10

